1. Field of the Invention
The present invention relates to an image forming apparatus, a control method thereof, and a process cartridge which is detachably attachable to the image forming apparatus.
The image forming apparatus herein embraces, for example, electrophotographic copying machines, electrophotographic printers (e.g., LED printers, laser beam printers, etc.), electrophotographic facsimile machines, electrophotographic word processors, and so on.
The process cartridge refers to a cartridge which integrally incorporates charging means, developing means, or cleaning means as process means acting on an image bearing body such as an electrophotographic, photosensitive body or the like, and the image bearing body and which is detachably attachable to the main body of the image forming apparatus, or a cartridge which integrally incorporates at least one of the charging means, developing means, and cleaning means, and the image bearing body and which is detachably attachable to the main body of the image forming apparatus, or a cartridge which integrally incorporates at least the developing means and the image bearing body and which is detachably attachable to the main body of the image forming apparatus.
2. Description of Related Art
Among the conventional image forming apparatus using the electrophotographic image forming process, such as the copying machines, laser beam printers, etc., there are maintenance-free image forming apparatus realized in such structure that a cartridge integrally incorporates the image bearing body such as the electrophotographic, photosensitive body or the like, and the process means acting on the electrophotographic, photosensitive body, e.g., a cleaning unit and/or a developing unit, and that the process cartridge is detachably attachable to the main body of the image forming apparatus.
In such image forming apparatus, for example, when a function of a component incorporated in the process cartridge is degraded after long-term use, the entire process cartridge is replaced. This replacing work is extremely simple work; for example, opening the main body of the image forming apparatus through a one-touch operation, removing an old process cartridge from the interior of the main body of the apparatus, and then mounting a virgin process cartridge onto the main body of the apparatus. Accordingly, a user can readily perform the replacing work by himself or herself, without depending upon a service person.
In the many conventional electrophotographic processes of the image forming apparatus as described above, triboelectrification (frictional charging) is used as a method of giving charge to toner as a developer. In general, a developing device carrying out the method of this type is provided with a developer carrying member of a roller shape for carrying and conveying a developer to an electrostatic, latent image formed on the electrophotographic, photosensitive body, and a developer layer thickness regulating member of a blade shape for applying the developer onto the developer carrying member.
For example, in the early stage of use of the process cartridge, however, the toner in the developing device is not rubbed sufficiently against such members as the developer carrying body and the developer regulating member and thus fails to bear sufficient charge, and there can occur a problem that the density is insufficient. In the case where the developing device is not used over a long period of time, charging on the toner can be attenuated and this can cause failure in forming an image of satisfactory density.
Further, as disclosed in Japanese Patent Application Laid-Open No. 10-307455, one of methods of charging the electrophotographic, photosensitive body by the use of charging accelerating particles is a method of supplying the charging accelerating particles from the interior of the developing device to a charging portion. In this charging method, however, since the charging accelerating particles are absent in the charging portion in the initial stage of the process cartridge, charging is insufficient, which can cause disturbance of images or the like due to charging failure. In order to avoid this problem, it is possible to provide the charging portion with some amount of charging accelerating particles in the production process. However, vibration or the like during transportation of the process cartridge can possibly peel off or deflect the charging accelerating particles preliminarily given to the charging portion, and thus this method cannot be considered as a sufficient countermeasure.